On the left and right hemisphere visual processing that precedes recognition.

Three experiments, and a replication of each, investigated the nonconscious prerecognition visual processing given left visual field (LVF) and right visual field (RVF) letter inputs. Each input was a vertically arrayed pair of letters in which three variables were manipulated: (1) the same letter twice vs one each of two letters, (2) same vs 180 degree difference in orientations within each letter pair, and (3) normal vs mirror-image letter form. The procedure presented all pairs of letter combinations in pairs of pre- and postmasked 10-msec flashes; the subject's task was to report which flash of each pair appeared to last longer. When letter pairs differed on all three variables, RVF presentations of mirror-image letters were judged to be longer than equal presentations of normal letters; the reverse occurred for LVF presentations. When one normal and mirror-image letter were presented, RVF presentations of mismatched orientations were judged to be longer than matched orientations, and the reverse was true for LVF presentations. When pairs of two normal letters were presented, no processing difference between LVF and RVF presentations was observed. A fourth experiment tested presence/absence detection of the letter pairs under the input conditions of the main experiments and showed those conditions to produce chance-level presence/absence detection. These results suggest that each hemisphere can perform its own prerecognition operations and that neither hemisphere is necessarily specialized for any particular prerecognition visual operation.

Perceptual processing of pattern goodness by left and right hemispheres.

Two experiments tested perceptual processing of Garner and Clement's (1963) good and poor five-dot patterns by the left and right hemispheres. Two (good) patterns were from four-member equivalence sets, and the other (poor) pattern was from an eight-member equivalence set. One of the good patterns formed a T shape that could be processed as a linguistic unit. In Experiment 1, 80 right-handed subjects made same-different judgments for lateralized 200-msec paired presentations of these patterns. When both presentations were to the RVF/LH, response latency was faster for the T pattern than for the other two. When both presentations were to the LVF/RH, response latency was faster for the two good patterns than for the poor pattern. When the first pattern was presented to the RVF/LH and the second was presented to the LVF/RH, response latencies were lower for the two good patterns than for the poor pattern. Also, when the first pattern was presented to the LVF/RH and the second was presented to the RVF/LH, response latency was faster for the T pattern than for the other good pattern which was, in turn, faster than for the poor pattern. Experiment 2 used a duration judgment task (Avant & Lyman, 1975) to test effects of pattern goodness on apparent durations of pre- and postmasked 10-msec pattern presentations. With left hemisphere inputs, presentations of good patterns were judged to be longer than presentations of the poor pattern. When each hemisphere compared the T and the other good pattern, presentations of the T pattern were judged to be longer, and the right hemisphere further discriminated among pattern orientations. Presentations of the T pattern to each hemisphere were judged to be longer than presentations of the poor pattern, and both hemispheres discriminated among orientations of both patterns. These results indicate that the two hemispheres can, during perceptual processing, function cooperatively, and that both prerecognition and conscious perceptual operations are guided by task demands.

Alcohol impairs visual presence/absence detection more for females than for males.

Ninety subjects (45 males, 45 females) were given 0.0, 0.5, or 1.0 ml/kg body weight of 190-proof ethanol and tested for chance-level presence/absence detection thresholds with energy-masked presentations of traffic signs and blank inputs. Alcohol produced higher blood alcohol concentration (BAC) levels, and higher detection threshold durations, for females than for males. These results indicate that alcohol influences precortical visual processing and that the influence is greater for females than for males. The higher bioavailability of alcohol in women is likely due to less gastric oxidation of ethanol in women than in men.

Stimulus familiarity modifies perceived duration in prerecognition visual processing.

Three experiments further explored the Avant, Lyman, and Antes finding that, during prerecognition processing, differences in subjects' familiarity with letters, words, and nonwords generate differences in the apparent duration of tachistoscopic flashes. The results replicate and extend the earlier findings, showing apparent duration differences with a variety of verbal stimuli over a range of tachistoscopic exposure intervals. The results also suggest that exposures of stimuli on early trials of an experiment reduce differences in preexperimental stimulus familiarity such that unfamiliar stimuli come to be processed more nearly like familiar stimuli. Familiarity acquired on early trials appears to accumulate at prerecognition levels of processing and to reduce apparent duration differences among stimuli on later trials.